Method and apparatus for cell identification for uplink interference avoidance using inter-frequency measurements

ABSTRACT

A method and system for cell identification for uplink interference avoidance that includes a network device and mobile device in a communications network. Inter-frequency measurements are performed by a mobile device on a downlink carrier currently not used by the mobile device. A result of the inter-frequency measurements is compared with another value. Second measurements are initiated on the downlink carrier currently not used by the mobile device based on the comparison. A cell is identified based on the second measurements. The inter-frequency measurements may include receive signal strength indicator (RSSI) measurements, received signal code power (RSCP) measurements, or average channel power-to-total signal power ratio (Ec/Io) measurements. The second measurements may include signal quality measurements.

[0001] This application claims the benefit of U.S. Provisional PatentApplication serial No. 60/375,813 filed Apr. 29, 2002, the contents ofwhich is expressly incorporated by reference herein.

BACKGROUND

[0002] 1. Field of the Invention

[0003] This invention relates to CDMA systems, and more specifically tocell identification using inter-frequency measurements in CDMA systems.

[0004] 2. Description of the Related Art

[0005] In Code Division Multiple Access (CDMA) systems, a soft handover(SHO) area is characterized by similarly strong pilot power signals(CPICH Ec/Io in Wideband CDMA (WCDMA)). Pilot powers are measured by themobile in idle as well as in connected mode. In connected mode, it isvery important that the mobile device (UE) is always connected to theoptimum cell(s). Otherwise, it would cause significant interference inuplink and waste network capacity. In idle mode, it is important to campin the strongest cell to allow a quick call initiation and not causeinterference during call initiation.

[0006] The uplink interference to the neighboring cells in WCDMA may beavoided with (1) soft handover within one frequency based on downlinkCPICH Ec/I0 measurements, or (2) “downlink dying first” with adjacentchannel interference. These methods work when there is a fixed pair ofuplink and downlink as in the UMTS core band in 2.1 GHz. This approachcannot be applied for 2.5 GHz when the same uplink carrier in 1.9 GHzcan be paired with downlink in 2.1 GHz or in 2.5 GHz. Therefore, newapproaches are needed to avoid the uplink interference.

SUMMARY OF THE INVENTION

[0007] A method and system for cell identification for uplinkinterference avoidance that includes a network device and mobile devicein a communications network. Inter-frequency measurements are performedby a mobile device on a downlink carrier currently not used by themobile device. A result of the inter-frequency measurements is comparedwith another value. Second measurements are initiated on the downlinkcarrier currently not used by the mobile device based on the comparison.A cell is identified based on the second measurements. Theinter-frequency measurements may include receive signal strengthindicator (RSSI) measurements, received signal code power (RSCP)measurements, or average channel power-to-total signal power ratio(Ec/Io) measurements. The second measurements may include signal qualitymeasurements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention is further described in the detaileddescription which follows in reference to the noted plurality ofdrawings by way of non-limiting examples of embodiments of the presentinvention in which like reference numerals represent similar partsthroughout the several views of the drawings and wherein:

[0009]FIG. 1 is a diagram of a system for soft handover detectionaccording to an example embodiment of the present invention;

[0010]FIG. 2 is a diagram of a potential interface scenario in an uplinkchannel according to an example embodiment of the present invention;

[0011]FIG. 3 is a diagram of another potential interface scenario in anuplink channel according to an example embodiment of the presentinvention;

[0012]FIG. 4 is a diagram of mobile node measurement activities duringdifferent mobile node states according to an example embodiment of thepresent invention;

[0013]FIGS. 5A and 5B are diagrams of uplink and downlink carrierpairings according to example embodiments of the present invention;

[0014]FIG. 6 is a graph illustrating soft handover area detection usingRSSI measurements according to an example embodiment of the presentinvention; and

[0015]FIG. 7 is a flowchart of a process for cell identificationaccording to an example embodiment of the present invention.

DETAILED DESCRIPTION

[0016] The particulars shown herein are by way of example and forpurposes of illustrative discussion of the embodiments of the presentinvention. The description taken with the drawings make it apparent tothose skilled in the art how the present invention may be embodied inpractice.

[0017] Further, arrangements may be shown in block diagram form in orderto avoid obscuring the invention, and also in view of the fact thatspecifics with respect to implementation of such block diagramarrangements is highly dependent upon the platform within which thepresent invention is to be implemented, i.e., specifics should be wellwithin purview of one skilled in the art. Where specific details (e.g.,circuits, flowcharts) are set forth in order to describe exampleembodiments of the invention, it should be apparent to one skilled inthe art that the invention can be practiced without these specificdetails. Finally, it should be apparent that any combination ofhard-wired circuitry and software instructions can be used to implementembodiments of the present invention, i.e., the present invention is notlimited to any specific combination of hardware circuitry and softwareinstructions.

[0018] Although example embodiments of the present invention may bedescribed using an example system block diagram in an example host unitenvironment, practice of the invention is not limited thereto, i.e., theinvention may be able to be practiced with other types of systems, andin other types of environments.

[0019] Reference in the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. The appearances of thephrase “in one embodiment” in various places in the specification arenot necessarily all referring to the same embodiment.

[0020] The embodiments of the present invention relate to WCDMAinter-frequency measurements. The embodiments will be illustrated usingan example extension band frequency (e.g., 2.5 GHz band) when allocatedfor WCDMA downlink. However, another possibility is a band allocation,where 1.7 and 2.1 GHz bands are may be used. Since the present inventionmay also cover a situation where 1.9 GHz operator may have a new band in2.1 GHz DL, but is not necessary intending to use 1.7 GHz UL at first.

[0021]FIG. 1 shows a diagram of a system for soft handover detectionaccording to an example embodiment of the present invention. The systemincludes a telecommunications network 10 that includes network devicesor nodes 12-22 and mobile devices (e.g., user equipment (UE), mobilenodes (MN), mobile stations (MS), etc.) 30-48. The terms mobile device,mobile node, and user equipment will be used interchangeably throughoutthe illustration of the embodiments of the present invention and referto the same type of device.

[0022] Network devices 12-22 may be any type of network node or devicethat supports wireless devices connected to a telecommunicationsnetwork, for example, a Radio Network Controller (RNC), a Base StationController (BSC), etc. Network device 12 and mobile device 36 transferdata and control information between each other via uplink 35 anddownlink 37 channels. A base station or cell (not shown) may supplyfrequencies from a particular band of frequencies that allow a mobiledevice 36 to select from and use for a downlink carrier and uplinkcarrier. The uplink carrier frequency and downlink carrier frequency maybe from the same band of frequencies, or from different bands offrequencies.

[0023] As a mobile device moves from one location to another, the basestation or cell closest to the mobile device will likely then supply theuplink and downlink carriers for the particular mobile device.Generally, if the same band of frequencies is available at theneighboring base station, the network device may direct a soft handoverto occur between the downlink and uplink carriers supplied from theoriginal base station to downlink and uplink carriers supplied from theneighboring base station.

[0024] According to the present invention, a currently used networkdevice 12 and/or neighboring network device 14, possibly along withmobile device 36, may detect soft handover areas before a handover is tooccur such that a handover may occur without causing uplink channelinterference. As noted previously, uplink interference may be causedwhen a mobile device moves to a location that does not supply the samebands of frequencies currently being used by the mobile device for itsdownlink carrier.

[0025] Each mobile device 30-48 and/or network device 12-22 may performvarious measurements in a periodic or continuous basis to detect softhandover areas for uplink interference avoidance. For example,measurements such as signal strength, signal quality, etc. may be madeand compared with similar measurements of carriers from neighboring orco-sited bands to determine if a soft handover area exists and whether ahandover should occur to avoid uplink interference. A network deviceand/or mobile device may determine the types of measurements made andwhen they are made. Moreover, a network device and/or mobile device mayperform the measurements, where in the latter case, a network node mayinstruct the mobile device to perform the measurements or the mobiledevice perform the measurements without instruction from the networkdevice. Further, the mobile device may perform the measurements andreport the results to the network device whereby the network devicedecides whether a soft handover area exists and whether a soft handovershould occur to avoid uplink interference.

[0026] Signal quality of a carrier (downlink or uplink) may includeinterference from other cells and is related to the signal quality at aspecific mobile device. In contrast, signal strength may include the sumof all the signals and indicates the total strength in a specificfrequency. With signal strength measurements, there is nodifferentiating between a particular mobile device's signal and othersignals. Co-sited downlink carriers are downlink carriers from the sameantenna or same base station or cell as the downlink carrier currentlybeing used by a mobile device.

[0027] Relative signal quality may also be a measurement performed. Inthis method, signal quality may be measured and compared with the signalquality of downlink carriers from another base station. Differencesbetween the two may be then used to determine if a soft handover areaexists. Moreover, a mobile device currently using a current downlinkcarrier from a current cell and moving closer to a neighboring cell maylook for a downlink carrier from the neighboring cell from the samefrequency band as the current downlink carrier. If a downlink carrier ismissing in this band, then the network device and mobile device knowthat a soft handover area exists where uplink interference may occur ifthe handover doesn't occur earlier.

[0028] Soft handover area detection may occur while a mobile device isin any mode or state, for example, the mobile device may be in an idlemode, or a connected mode where it is waiting for data or activelytransmitting data. Depending on the mode or state of the mobile device,may determine what types of measurements (e.g., inter-frequencymeasurements) may be made.

[0029] One reason for handover may be because the mobile device hasreached the end of coverage of a frequency carrier in an extension(e.g., 2.5 GHz) band. The end of extension band coverage may invokeinter-band, inter-frequency or inter-system handover. The triggercriteria may always be the same. As inter-band handovers can possibly bedone faster, separate trigger thresholds might be implemented. Someexample coverage triggers for example implementations according to thepresent invention may include but are not limited to: handover due toUplink DCH quality, handover due to UE Tx power, handover due toDownlink DPCH power, handover due to common pilot channel (CPICH)received signal code power (RSCP), and handover due to CPICH chipenergy/total noise (Ec/No).

[0030] Coverage may be another reason for handover. A coverage handovermay occur if: (1) the extension band cell has a smaller coverage area(=lower CPICH power or different coverage triggers) than a core band,(2) currently used core band coverage ends (then also extension band),or (3) the UE enters a dead zone.

[0031] Intra-frequency measurements may be another reason for softhandover. A soft handover procedure in an extension band may work inprinciple the same way as in core bands with branch addition,replacement and deletion procedures. SHO procedures may be based onCPICH Ec/I0 measurements. Despite stronger attenuation in the extensionband, Ec/I0 as a ratio may be about the same for both bands. Therefore,in principle the same SHO parameter settings may be used in theextension band. However, if stronger attenuation in an extension band isnot compensated for by additional power allocation, the reliability ofSHO measurements (Ec/Io) may suffer. Moreover, an extension band cellmight have neighbors on extension band frequencies and on core bandfrequencies at the same time. Then, the UE may have to measure bothintra-frequency and inter-band neighbors.

[0032] UL interference in the core bands due to delayed soft HO at theextension band coverage edge may occur. An extension band cell may haveboth extension band neighbors and core band neighbors at the same time.While for the extension band neighbor the normal SHO procedure may besufficient, for the core band neighbor an early enough inter-bandhandover may have to be performed. Otherwise, serious UL interferencecould occur in the core band neighbor cell. SHO areas might be locatedrelatively close to the base station and thus not necessarily relate tohigh UE Tx (transmit) power (or base transceiver station (BTS) Txpower). Coverage handover triggers may not be sufficient.

[0033]FIG. 2 shows a diagram of a potential interface scenario in anuplink channel according to an example embodiment of the presentinvention. Three cells or base stations 51, 53, 55 are shown with slightintersection between neighboring (adjacent) coverage areas. The leftmostcell 51 supplies two co-sited bands of frequencies, an extension band offrequencies 60 and a core band of frequencies 54. The middle cell 53also supplies two co-sited bands of frequencies, an extension band offrequencies 52 and a core band of frequencies 56. The rightmost cell 55only supplies a core band of frequencies 58.

[0034] In this example embodiment, a mobile device (UE) 50 is using adownlink carrier from an extension band of frequencies 52 from basestation 53 closest to the mobile device 50. As a mobile device 50 movesfrom the left side of base station 53 and approaches cell coverageoverlap areas, the mobile device uses UL and DL carriers fromneighboring cells (i.e., middle cell 53 and rightmost cell 55).Generally, if the mobile device 50 is using an UL and DL carrier in anextension band (e.g., a band of frequencies starting at approximately2.5 GHz) cell, once the mobile device 50 moves towards the coverage of aneighboring extension band cell, a soft handover will occur between theDL and UL carriers of the neighbor cells. However, in a situation wherethere is no neighboring extension band cell as shown here, a softhandover cannot occur since the mobile device 50 must now obtain a DLand UL carrier from a core band (e.g., a band of frequencies starting atapproximately 2 GHz) cell. This may cause interference in the UL carrier(not shown) of the neighboring cell. However, according to the presentinvention, a network device may monitor this situation and causeselection of a different DL carrier in an existing band early to allow asoft handover from the extension band 52 (e.g., 2.5 GHz) in middle cell53 to the core band 58 (e.g., 2.0 GHz) in the neighboring cell 55,therefore, avoiding potential interference in the UL carrier of theneighboring cell 55.

[0035]FIG. 3 shows a diagram of another potential interface scenario inan uplink channel according to an example embodiment of the presentinvention. In this example embodiment, a mobile device (UE) 50 is usinga downlink carrier from a core band of frequencies 58 from base station55. Mobile device may not make a soft handover to an extension band 52from base station 53 since the mobile device 50 will be jumping into apotential interference area, causing UL channel interference. Accordingto the present invention, this situation is detected and earlierdecisions made regarding handover to avoid UL channel interference.

[0036] In order to prevent a directed RRC connection setup into aninterfering area, the UE (mobile device) may need to report in a RACHmessage the measured neighbors in the core band. The message attachmentmay be standardized but may need to be activated. A network node (e.g.,Radio Network Controller (RNC)) then may need to check that all measuredcells have a co-sited neighbor in the extension band.

[0037] Adjacent cell interference (ACI) detection before the directedsetup is automatically given if FACH decoding in the core band wassuccessful. Load reason handover may be needed in addition to DirectedRRC connection setup for congestion due to mobility. The load reasonhandover in current implementations is initiated by UL and DL specifictriggers. By setting the trigger thresholds the operator can steer theload balancing:

[0038] for load threshold for RT users, in UL the total received powerby the BTS relative to the target received power (PrxTarget) and in DLthe total transmitted power of the BTS relative to the targettransmitted power (PtxTarget);

[0039] for NRT users: rate of rejected capacity requests in UL & DL;

[0040] Orthogonal code shortage.

[0041] In 2.5 GHz operation, UL load may only be balanced byinter-frequency and inter-system handovers whereas DL load may bebalanced in addition by inter-band handovers. So, when consideringinter-band handovers (UL stays the same) only DL triggers may beimportant.

[0042] Therefore, FIGS. 2 and 3 show that in an extension band (e.g., aband with frequencies starting at approximately 2.5 GHz) edge cells,both intra-frequency measurements for soft handover and continuousinter-frequency measurements (CM) may be needed. One way to guaranteeavoidance of UL interference in a core band (e.g., a band withfrequencies starting at approximately 2.0 GHz) SHO area is tocontinuously monitor the core band DL CPICH Ec/Io in the cells whereneeded, (i.e., in coverage edge cells), and if a SHO area in the coreband is detected initiate an inter-band handover.

[0043] In contrast, an inter-band handover core band-to-extension bandmay not occur in cells underlying a extension band coverage edge cell ifthe UE is in a SHO area. Specifically, a load/service reason inter-bandhandover during SHO in core bands may not be allowed. Also, inter-bandhandover core band-to-extension band due to an unsuccessful softhandover (branch addition) procedure may be disabled, butinter-frequency HO allowed.

[0044] Compressed mode may also be used for avoidance of adjacentchannel protection (ACP)-caused UL interference. ACP caused ULinterference may occur at certain UE Tx power levels where the UElocation is close to an adjacent band base station. This is mostly amacro-micro base station scenario. The interfered base station may beprotected in DL if it is operating in the adjacent extension bandcarrier otherwise not.

[0045] Adjacent channel interference (ACI) probability may directlyrelate to the mobile device's transmission power. Below certain powersthe mobile cannot interfere to the micro base station and interferencedetection may not be required. A reasonable value for the powerthreshold that determines when to start interference detection may needto take into account the statistical probability of MCL (minimumcoupling loss) situations, adjacent channel leakage power ratio (ACLR),micro BTS noise level and desensitization. If the power is around theaverage UE Tx power (=−10 . . . 10 dBm) or higher, the number of mobiledevices continuously checking for ACI interference may be reducedsignificantly.

[0046] An interfered base station may not be able to protect itself fromACI interference. The interfering mobile device must voluntarily stoptransmission on its current band. Only by also operating in an extensionband is the interfered base station self-protected.

[0047] Regarding compressed mode operation in an extension band(Cell_DCH), when the UE is operating in the extension band and needs tomeasure the core DL bands, CM usage in the core band can be appliednormally and balancing of UL load may be triggering separatelyinter-frequency measurements. As described previously, there may beseveral reasons for inter-band CM measurements when the UE is in theextension band.

[0048] Since the DL load of the other band may be known, a networkdevice (e.g., RNC) may initiate instead of an inter-band handoverdirectly, an inter-frequency or inter-system handover in case of highload. Then, separate inter-frequency/inter-system measurements may beperformed. In order to minimize the effects on network performance, CMmay need to be used very efficiently and one consistent CM usagestrategy may need to cover all inter-band measurements. The mostexcessive CM usage may come from “ACI detection” and “SHO areadetection”. Both of these may be continuous in case they are needed.Both may be largely avoided either by intelligent carrier allocation inthe extension band or by network planning.

[0049] Most of the carriers may be protected by carrier allocation. Onlyif an existing operator is not interested in extension band (e.g., 2.5GHz) deployment, the UL adjacent carriers may need the ACI detection toprotect another carrier from UL interference. Also, if operators want tohave different numbers of extension band carriers, at some point, the ULcarrier pattern may not be repeatable anymore in the extension band.Further, since a first operator may not use its additional carriers inthe same geographical area and starting at the very same time as asecond operator, ACI detection may be needed wherever protection fromthe extension band adjacent carrier is not provided.

[0050] UL carriers in the TDD band may be automatically protectedbecause here the UL carrier may exist only if also extension band isdeployed. However, the adjacencies between TDD band and UL band may needspecial attention as again a first UL carrier can be interfered by asecond if it is not (yet) operating in the extension band.

[0051] Regarding SHO area detection, network planning can reduce theneed of CM by limiting the number of extension coverage edge cells andindicating edge cells via RNP parameters. If sectorized cells in thecore band are fully repeated in the upper band, i.e., no softer handoverarea in the UL that is not a softer handover area in the extension band,the detection of SHO areas may be made dependent on the UE transmissionpower or CPICH Ec/Io. However here, it is more difficult to determine athreshold since there is no general limitation how close base stationscan be to each other. If almost complete extension band coverage isneeded it might be wise not to save on single sites and rather make thecoverage as complete as possible. Moreover, if sparse capacity extensionis needed, one can consider having less coverage area in the extensionband cell by lowering the CPICH pilot power or applying differentcoverage handover thresholds. This lowers the average UE transmissionpower in the sparse cell and thus the probability of ACI or unwantedentering in UL SHO area.

[0052] Non-regarding network planning, there are still some cells whereall reasons for CM are given. Here, the CM usage must be made efficient.

[0053] Most all reasons for CM require measurement of the associated DLcore band, either own cell or neighbors. ACI detection can also beobtained by measuring the received signal strength indicator (RSSI) ofthe adjacent carriers in the core. If both SHO area detection and ACIdetection is needed, it may be more efficient to rely for both on Ec/Iomeasurements provided that latter measurement can be done quicklyenough. This may be enabled for two reasons: (1) CM in extension bandoperation can use the fact that extension band DL and core band DL arechip synchronized (assuming they are in the same base station cabinet,i.e., co-sited), and (2) both DL bands have the same or at least verysimilar propagation path differing merely in stronger attenuation forthe extension band.

[0054] Two options for chip energy/system noise measurements mayinclude: (1) measure core band average channel power-to-total signalpower (Ec/Io) (fast due to chip synchronization)—more accurate, mayrequire a measurement gap of 4-5 timeslots, and (2) measure core bandRSSI and use CPICH Ec correlation between bands =>Ec/Io—may require ameasurement gap of 1-2 timeslots.

[0055] The second option may be preferred due to the short gaps.Basically, not even level measurements (Ec/Io) are required if therelative difference between both DLs RSSI is considered. Uncertaintieson the network side (antenna pattern/gain, cable loss, loading, PArating, propagation loss/diffraction) as well as on the UE side(measurement accuracy) may disturb the comparison and may need to betaken into account if possible.

[0056] If a high difference in RSSIs (or low Ec/Io in the core band) isdetected, the reason may be verified by:

[0057] measure associated core cell's neighbors →if SHO area (little i)make inter-band handover;

[0058] measure adjacent channel RSSI →if ACI make inter-frequency HO;

[0059] none of above true →no action required (associated core cell'sload might be high).

[0060] In case (a), handover happens directly to a SHO area. This mayrequire a fast enough branch addition after the inter-band hardhandover.

[0061] Additionally, CM usage can be minimized by triggering it withsome kind of UE speed estimate. If a UE is not moving CM can be ceased,when it moves again CM continues.

[0062] Regarding measurements for cell re-selection when the extensionband is used, the UE in idle mode camps in the extension band as long asEc/Io signal is good enough. In connected mode, PS services move toCell_FACH, UTRAN registration area routing area paging channel(URA_PCH), or Cell_PCH state after a certain time of inactivity (NRT).Then, idle mode parameters may control the cell re-selection. Cellre-selection may then happen for a coverage reason, i.e., when theextension band's coverage ends.

[0063] Interference detection may need to be provided also in statescontrolled by idle mode parameters to prevent UL interference due toRACH transmission. Here, for ACI and SHO area detection differentmechanisms may be applied.

[0064] SHO area detection in idle mode (and Cell_PCH, URA_PCH) may beenabled by a two-step measurement and applied to the coverage edgecells: (1) a cell specific absolute Ec/Io-threshold triggers step, and(2) measure core band whether there is a cell without inter-bandneighbor in extension band. To make the comparison, the UE may need toknow the co-sited core neighbors. This may need to be added in extensionband broadcast channel system information (BCCH SI). In Cell_FACH state,SHO areas may be detected by using the IF measurements occasions andchecking if found neighbors in the core band have a co-sited neighbor inthe extension band. Again additional BCCH information may be needed.

[0065]FIG. 4 shows a diagram of mobile node measurement activitiesduring different mobile node states according to an example embodimentof the present invention. The different states of the mobile device areshown inside arrows at the top of the figure. The mobile device may bein idle state, cell FACH state, or cell DCH state. The timeline shown inFIG. 4 is divided in half where the top half represents measurements todetect soft handover (SHO) area, and the bottom half representsmeasurements to detect adjacent channel interference (ACI). The variousmeasurements that occur for each area and during each state of themobile device along the time line are shown inside the call-outs.

[0066] ACI may not be detected in idle mode but immediately before RACHtransmission by measuring directly the two neighboring (adjacent)carriers in the core band. The delay in RACH transmission may benegligible due to the fast RSSI measurements. In Cell_FACH state, ACIdetection may be provided by continuously measuring the adjacent corecarriers (stealing slots for RSSI measurements).

[0067] In the case of the SHO area, the UE may initiate an inter-bandhandover to the core band. In case ACI is detected, the UE may initiatean inter-frequency handover (UL changes) similar to a conventionalcoverage reason cell re-selection.

[0068]FIGS. 5A and 5B show diagrams of uplink and downlink carrierpairings according to example embodiments of the present invention.Uplink and downlink carriers from the existing band generally may befrequencies supplied by the same cell, but may be supplied fromdifferent cells. Similarly, uplink and downlink carriers from the newband may be frequencies supplied from the same cell (different from thecell supplying existing band frequencies). The A1, A2, A3, . . .represent different uplink/downlink frequency pairings. The frequenciesin the box for each band starting with “A′”, may be controlled by oneoperator at the cell, the frequencies in the blank boxes controlled by asecond operator at the cell, and the frequencies in the darkened boxescontrolled by a third operator at the cell.

[0069] In these example embodiments, the existing uplink frequency bandis shown to include frequencies starting at approximately 1920 MHz, theexisting downlink band to include frequencies starting at approximately2110 MHz, and the new uplink and downlink bands to include frequenciesstarting at approximately 2500 MHz. However, the present invention isnot limited by these frequency values but may be applied to any bands ofpossible frequencies. The frequencies being shown in FIGS. 5A and 5Bhere are for illustration purposes only, and does not limit the scope ofthe present invention.

[0070]FIG. 5A shows an example embodiment where a mobile node (UE) maybe connected with a uplink carrier frequency from an existing uplinkband 60 and a downlink carrier frequency from an existing downlink band62. The existing downlink carrier band 62 may be a core band from a cellclosest to the location of the mobile node. A network node may determinethat the mobile node should select a second downlink carrier, and directthe mobile node to start using a downlink carrier from frequencies in anew or different downlink band 64 (i.e., from a different cell). Themobile node may then use the uplink carrier from the existing band 60and a downlink carrier from a new or different downlink band 64.

[0071]FIG. 5B shows an example embodiment where a mobile node may haveoriginally been using an uplink carrier from a new uplink band 66 and adownlink carrier from a new downlink band 68. The new uplink band andnew downlink band may be from the same band of frequencies (e.g.,starting at approximately 2.5 GHz where some frequencies are used foruplink carriers and some for downlink carriers). In this exampleembodiment, a network node may direct the mobile device to switch overand use a different downlink carrier, but from the same band offrequencies as the original downlink carrier. The frequencies in the newuplink band 66 and the new downlink band 68 may be supplied by the samecell, or from different cells.

[0072] According to embodiments of the present invention,inter-frequency measurements may be performed to identify cells andavoid potential interference scenarios. Initially, inter-frequencymeasurements for co-sited cells are performed. These measurements mayinclude receive signal strength indicator (RSSI) measurements (1-2 slotgaps), received signal code power (RSCP) measurements (4-5 slot gaps),average channel power-to-total signal power ratio (Ec/Io) measurements(4-5 slot gaps), etc. RSSI measurements may be preferred since thesemeasurements are fast since they do not require any synchronization tothe other carrier but just the total power is measured. This measurementmay be completed in 1-2 slots. Next, cells on other frequencies may beidentified based on the results of the measurements. This may take moretime since the mobile device may need to identify the scrambling codeand timing of the cell by typically utilizing a primary synchronizationchannel (P-SCH), a secondary synchronized channel (S-SCH) and/or aprimary common pilot channel (P-CPICH). Typically, this measurement maybe activated by a network device (e.g., radio network controller (RNC))with compressed mode.

[0073] An event triggered reporting could be defined for the mobiledevice to report the RSSI measurement once the result of a measurementexceeds a predefined value. The reporting threshold may be based on themobile device transmit (TX) power.

[0074] The cells on other frequencies being identified may be skipped ifthe inter-frequency measurements (e.g., RSSI) do not indicate any strongsignal in that frequency. The inter-frequency measurement may be alsocombined with the information in the network (like load) to decidewhether cells on other frequencies need to be identified.

[0075]FIG. 6 shows a graph illustrating soft handover area detectionusing RSSI measurements according to an example embodiment of thepresent invention. This graph shows an x-axis representing location(i.e., the movement of the mobile device), and a y-axis that representsRSSI. The two curves 100 102 represent a measured RSSI at a givenlocation for a frequency on channel 1 of a first cell 106 and afrequency on channel 1 from a second cell 108, respectively. Dashed line104 represents a thermal noise level at the mobile device. As can beseen in the figure, as the mobile device moves, the RSSI of thefrequency 100 from the first cell 106 may begin to decrease relative tothe RSSI of the frequency 102 from the second cell 108. Inter-frequencymeasurements (RSSI in this example) and comparison of the measurementsto a threshold value or the measured value of the frequency currentlyused by the mobile device (as shown here) may reveal the existence ofanother cell, cell2, 108 (i.e., the second cell). Therefore, handovermay be initiated to avoid uplink interference.

[0076] Two examples using RSSI, one for soft handover area detection andanother for adjacent channel interference detection, will be used tofurther illustrate that inter-frequency measurements (specifically RSSIin this example embodiment) may be used to detect the existence of thedownlink before the uplink can cause any interference problems.

[0077] Regarding the first example, when an extension band (e.g., 2.5GHz) downlink connection is used, the downlink CPICH Ec/Io measurementsmay not be able to be used to detect the soft handover area at the edgeof the extension band coverage area. Therefore, the mobile device mayneed to make periodic inter-frequency measurements on the continuouscoverage core band (e.g., 2.1 GHz) downlink carrier. The presentinvention may be used to trigger the compressed mode measurements, andhence reduce the measurement time with compressed mode. If the RSSImeasurements in 2.1 GHz shows that there is a higher received signalpower than in 2.5 GHz, the reason can be another cell on the samefrequency.

[0078] Assuming, for example, that: mobile device noise level=100 dBm,UE max uplink power=21 dBm and BTS min transmission power CPICH=33 dBm,the maximum interference level that the mobile device can cause inuplink at the moment it is able to detect the DL ch1neighbor=21−(33+100)=−112 dBm which is below a BTS noise level.Therefore, we can conclude that a RSSI measurement is able to show theexistence of the other cell before the mobile device can causeinterference in that cell.

[0079] Regarding the second example, when the 2.5 GHz downlinkconnection is used, the downlink does not get dropped because of theadjacent channel interference in 2.1 GHz and the mobile device mayinterfere the uplink of the adjacent carrier in 1.9 GHz. Assuming, againfor example, mobile device noise level=100 dBm, mobile device max uplinkpower=21 dBm, mobile device ACS and ACLR=33 dB, and BTS min transmissionpower CPICH=33 dBm (worst case assumption for interfered base station),the maximum interference level that the mobile device can cause inuplink to the adjacent carrier at the moment it is able to detect theother base station=21−33−(33−33+100)=−112 dBm which is below BTS noiselevel. Therefore, we can conclude that a RSSI measurement is able toshow the existence of the adjacent frequency before the mobile devicecan cause interference in that cell.

[0080]FIG. 7 shows a flowchart of a process for cell identificationaccording to an example embodiment of the present invention.Inter-frequency measurements are performed by a mobile device on adownlink carrier currently not used by the mobile device S1. A result ofthe inter-frequency measurements is compared with another value S2.Second measurements are initiated on the downlink carrier currently notused by the mobile device based on the comparison S3. A cell isidentified based on the second measurements S4.

[0081] The inter-frequency measurements may include receive signalstrength indicator (RSSI) measurements, received signal code power(RSCP) measurements, or average channel power-to-total signal powerratio (Ec/Io) measurements. The second measurements may include signalquality measurements.

[0082] The result of the inter-frequency measurements may be comparedwith a threshold value or with a value from a measurement of a downlinkcarrier currently used by the mobile device. Moreover, the result of theinter-frequency measurements may be reported to the network via anetwork device, e.g., a radio network controller (RNC) or a base stationcontroller (BSC).

[0083] More detailed inter-frequency measurements may be initiated.These detailed measurements may include compressed mode measurements.The cell may then be identified based on the more detailedinter-frequency measurements. The detailed inter-frequency measurementsmay include signal quality measurements, e.g., CPICH Ec/Io measurements.

[0084] The value may be set at the mobile device by the network devicein advance, or dynamically set based on the current network conditionsor based on characteristics of the mobile device.

[0085] The downlink carrier currently used by the mobile device may bein an extension band of frequencies, e.g., a band of frequenciesstarting at approximately 2.5 GHz. The method downlink carrier notcurrently used by the mobile device may be in a core band offrequencies, e.g., a band of frequencies starting at approximately 2GHz.

[0086] The cell may be identified by identifying the scrambling code andtiming of the cell utilizing a primary synchronization channel (P-SCH),a secondary synchronized channel (S-SCH), or a primary common pilotchannel (P-CPICH). Moreover, the network device or the mobile device mayinitiate the identifying of the cell.

[0087] The present invention is advantageous in that it allows for theavoidance of severe interference scenarios. Moreover, uplinkinterference avoidance according to the present invention allows for newfrequencies from new bands to be used for uplink and downlink carriers.

[0088] It is noted that the foregoing examples have been provided merelyfor the purpose of explanation and are in no way to be construed aslimiting of the present invention. While the present invention has beendescribed with reference to a preferred embodiment, it is understoodthat the words that have been used herein are words of description andillustration, rather than words of limitation. Changes may be madewithin the purview of the appended claims, as presently stated and asamended, without departing from the scope and spirit of the presentinvention in its aspects. Although the present invention has beendescribed herein with reference to particular methods, materials, andembodiments, the present invention is not intended to be limited to theparticulars disclosed herein, rather, the present invention extends toall functionally equivalent structures, methods and uses, such as arewithin the scope of the appended claims.

What is claimed is:
 1. A method for cell identification for uplinkinterference avoidance comprising: performing inter-frequencymeasurements by a mobile device on a downlink carrier currently not usedby the mobile device; comparing a result of the inter-frequencymeasurements with another value; initiating second measurements on thedownlink carrier currently not used by the mobile device based on thecomparison; and identifying a cell based on the second measurements. 2.The method according to claim 1, further comprising comparing the resultof the inter-frequency measurements with a threshold value.
 3. Themethod according to claim 1, further comprising comparing the result ofthe inter-frequency measurements with a value from a measurement of adownlink carrier currently used by the mobile device.
 4. The methodaccording to claim 1, further comprising reporting the result of theinter-frequency measurements to a network device.
 5. The methodaccording to claim 1, further comprising initiating more detailed secondmeasurements using compressed mode measurements and identifying the cellbased on the more detailed second measurements.
 6. The method accordingto claim 1, wherein the second measurements comprise signal qualitymeasurements.
 7. The method according to claim 6, wherein the signalquality measurements comprise CPICH Ec/Io measurements.
 8. The methodaccording to claim 1, further comprising setting the value at the mobiledevice by the network device in advance.
 9. The method according toclaim 1, wherein a downlink carrier currently used by the mobile deviceis in an extension band of frequencies.
 10. The method according toclaim 9, wherein the extension band of frequencies comprises frequenciesstarting at approximately 2.5 GHz.
 11. The method according to claim 1,wherein the downlink carrier not currently used by the mobile device isin a core band of frequencies.
 12. The method according to claim 11,wherein the core band of frequencies comprises frequencies starting atapproximately 2 GHz.
 13. The method according to claim 1, furthercomprising identifying the cell by identifying the scrambling code andtiming of the cell utilizing at least one of a primary synchronizationchannel (P-SCH), a secondary synchronized channel (S-SCH), and a primarycommon pilot channel (P-CPICH).
 14. The method according to claim 1,wherein the network device initiates the identifying of the cell. 15.The method according to claim 1, wherein the inter-frequencymeasurements comprise received signal strength indicator (RSSI)measurements.
 16. The method according to claim 1, wherein theinter-frequency measurements comprise received signal code power (RSCP)measurements.
 17. The method according to claim 1, wherein theinter-frequency measurements comprise average channel power-to-totalsignal power ratio (Ec/Io) measurements.
 18. A system for cellidentification for uplink interference avoidance comprising: a networkdevice in a communications network; and a mobile device, the mobiledevice operatively connected to the communications network and using adownlink channel, wherein inter-frequency measurements are performed bythe mobile device on a downlink carrier currently not used by the mobiledevice and a result of the measurements compared with another value,second measurements being initiated on the downlink carrier currentlynot used by the mobile device based on the comparison, a cell beingidentified based on the second measurements.
 19. The system according toclaim 18, wherein the result of the inter-frequency measurements arecompared with a threshold value.
 20. The system according to claim 18,wherein the result of the inter-frequency measurements are compared witha value from a measurement of a downlink carrier currently used by themobile device.
 21. The system according to claim 18, wherein the resultof the inter-frequency measurements are reported to a network device.22. The system according to claim 18, wherein more detailed secondmeasurements using compressed mode measurements are initiated and thecell is identified based on the more detailed second measurements. 23.The system according to claim 18, wherein the second measurementscomprise signal quality measurements.
 24. The system according to claim18, wherein the network device comprises one of a radio networkcontroller (RNC) and base station controller (BSC).
 25. The systemaccording to claim 18, wherein one of an inter-frequency handover and aninter-system handover are launched from the current downlink channelthus avoiding interference in an uplink channel not currently used bythe mobile device.
 26. The system according to claim 18, wherein theinter-frequency measurements comprise received signal strength indicator(RSSI) measurements.
 27. The system according to claim 18, wherein theinter-frequency measurements comprise received signal code power (RSCP)measurements.
 28. The system according to claim 18, wherein theinter-frequency measurements comprise average channel power-to-totalsignal power ratio (Ec/Io) measurements.